Normally a surround system uses a single speaker for the center channel, but I have always considered that the main flaw in the design. In most home setups, the sound comes from above or below the screen and I find that very distracting. Most people get used to it and the brain compensates by creating a virtual audio image across the screen. In my case, that has never happened. My solution was to use a Yamaha receiver that has an ambience channel. This is comprised of 2 extra speakers that enhance the sound by creating extra ambiance, but also has the ability to add center channel information to those 2 speakers. When placed correctly, these extra speakers will bring the center channel information up to the center of the screen. It works very well.

I have Magnepan wall speakers and I was reading about using their center channel speakers with two additional wall speakers flanking both sides of the screen to get the same effect that I mentioned above. All their speakers are 5 ohm. The way they set it up was to wire the 2 wall speakers in series (10 ohms) and then wire the center speaker in parallel with those two for a combined impedance of 3.3 ohms. My receiver is rated at 6/8 ohms, but the specs also shows a peak output at 2 ohms. In addition, I understand that the Magnepans impedance is lowest below 200 Hz. I set the speakers to small and the crossover to 200 Hz to reduce the current to these speakers. Also, because there are now three speakers, the volume was reduced accordingly to match the main speakers. Still, I can't get it out of my mind that at times the current draw is going to be excessive and shorten the life of the receiver.

I then wired all 3 of the speakers in series for a total of 15 ohms impedance. I actually liked this way better because now all 3 speakers are at the same volume, whereas before in the previous setup, the 2 wall hanging speakers were not as loud as the center channel speaker. I realize that I have to increase the preamp section of the center channel higher than the main speakers which in turn makes that channel the limiting factor of the maximum output of the entire system (at least I assume so). I have yet to run out of power so I don't believe this to be an issue. I believe this solves the problem with too high a current drain compared to the previous configuration.

This brings me to my question...

Is it okay to run speakers at 15 ohms and is there anything else that I need to be concerned about? Is my logic correct?

You might be asking, if the ambiance speakers worked so well, why would I want to do this? The answer... The ambiance speakers only do their magic when they are engaged. If I wanted to run without them and just with Dolby or DTS, they do not function. Also I cannot run 7.1 surround and the ambiance channels at the same time. Besides, I already had an extra pair of Magnepan speakers stored away that I wasn't using.